In pulsed operation of gaseous discharge devices such as flashlamps which are used as laser pump sources, there is often a need for circuitry to maintain the gaseous discharge device in continuous conduction between pulse operations in order to stabilize the operation of the gaseous discharge device. One of the most common types of gaseous discharge devices is a flashlamp which typically contains xenon or krypton gas. These types of flashlamps are typically used as laser pump sources and, for purposes of discussion of the instant invention, the flashlamp will be used as a representative gaseous discharge device. Flashlamp impedance, and the impedance of similar gaseous discharge devices, is highly non-linear and, for low currents, is negative. In order for a flashlamp to remain in continuous conduction, it must be supplied with power from a source having a larger internal impedance than the negative dynamic impedance of the flashlamp itself. In the past, the simplest type of simmering power supply was simply a high voltage DC source with a large series resistor placed between the source and the flashlamp to control current into the lamp. This type of design is simple but requires considerable power dissipation to achieve stable operation. For example, using a 10,000 ohm resistor, simmering of a typical flashlamp may be achieved at 100 mA. The lamp voltage may be approximately 200 volts, thus a 1,200 volt source at 100 mA might be required to achieve reliable simmering with a total dissipation of 120 watts.
Another approach which offers a significant reduction in the power dissipation entailed in the previously described series resistor circuit, utilizes a switching pre-regulator which passes a constant current to the input of a DC to DC converter. This type of simmering power supply produces large amounts of ripple current in the flashlamp and requires 60 to 80 mA for reliable simmering. The overall efficiency is roughly 65% resulting in approximately 22 watts of total power dissipation and approximately 50 circuit components. Other types of simmering circuits are available which offer improvements in power dissipation compared to the series resistor circuit, but achieve this improvement at the expense of simplicity since these circuits are typically complex and require high component counts.
Simmering power supplies typically find use in laser rangefinders and other tactical systems which employ pumped lasers. In portable systems, power dissipation is a very important parameter since operating power is supplied typically by batteries. Additionally, all power dissipation results in heat which must be removed in order to prevent excessive temperature build up. Reliability is also extremely important and, as is well known, reliability usually decreases as complexity increases. Accordingly, what is needed is a simple, reliable simmering power supply which utilizes few components and minimizes power dissipation. The instant invention offers an optimal solution to all these needs by presenting a very simple circuit with a lower component count which can maintain a flashlamp or other similar gaseous discharge device in a simmering condition between pulsed operations with greatly reduced power dissipation.